Various optical filters such as optical low pass filters are used in image-taking devices such as video cameras and digital still cameras. Such filters perform a role of removing light of unnecessary wavelengths such as infrared light and wave-filtering optical false signals. Using an example of an optical low pass filter, commonly used configurations of such optical filters include configurations in which plates such as a quartz birefringent plate and an infrared cut glass plate are appropriately combined according to desired wave-filtering characteristics. And in recent years, depending on an application, configurations in which an optical interference film is formed on a single plate are also being used. In the case of a configuration in which a plurality of plates are combined, conventionally manufacture of such optical filters involved using an adhesive to individually laminate the optical plates to be combined, which were divided into small pieces.
However, in recent years, as shown in JP H9-43542A for example, a so-called multi-cutout manufacturing method has been proposed and implemented, which involves laminating necessary structural members according to required wave-filtering characteristics at a stage prior to cutting of the wafer into small pieces, then performing cutting to obtain individual optical filters. Reductions in manufacturing costs have been achieved with manufacturing methods such as this.
On the other hand, cut edge portions of an optical filter made with this multi-cutout manufacturing method are sharp. These edge portions are often cracked or chipped when viewed microscopically, and there is a possibility that some of the optical plates will suffer from further chipping or cracking. In this case, cracked pieces or chipped pieces may adhere to a main surface of the optical plate, which is a transmission surface for optical information, and become optical foreign substances. Such foreign substances may be picked up by image-taking elements such as a CCD and become a cause of worsened image quality during video output.
Furthermore, other members may be cut when the edge portions are sharp and such cut pieces can become optical foreign substances. For example, it is common for optical filters to be storage packed in a resin case for delivery to a customer, and edge portions can cut into an inner wall of the resin case due to looseness within the storage case, thus resulting in cut pieces adhering to a main surface of an optical plate. Configurations have been disclosed with regard to preventing such looseness, such as JP 2000-238877A, in which side surfaces of an optical filter are fixedly supported, and JP 2001-2167A, in which the optical filter is fixed with an adhesive sheet. However, optical foreign substances also can be produced by contact with a case when optical filters are taken out from the case to be moved individually.
As a countermeasure against such optical foreign substances, Japanese Utility Model No. 2508176 discloses a configuration in which chamfering that forms a linear slanted surface is performed with respect to edges formed on an optical filter. Although such a chamfered structure is not sharp, edges are still formed, and these edge portions may be affected by cracking or chipping, thus resulting in pieces being cut from a resin case as mentioned above.
And furthermore, due to continued miniaturization of image-taking devices such as video cameras, a distance between a front surface of a CCD and an optical filter positioned thereon has been becoming shorter in recent years. And in this case, optical foreign substances that have adhered to a main surface of the optical filter cause even more conspicuous image defects, leading to worsened image quality during video output.